startup-config file open failed (Not enough space)

Stack of four Catalyst 2960S switches on 15.0(2)SE6.

I made one change, issued wr me and then made another change, and attempted to write mem again. After the second change, I get the error:

startup-config file open failed (Not enough space) 

According to this forum post, fix is to change buffer size and reboot if nvram is not corrupt.

I have plenty of memory:

dir flash: Directory of flash:/ 3 -rwx 3076 Feb 2 2018 11:59:02 -06:00 vlan.dat 4 -rwx 4050 Jan 17 2018 12:06:38 -06:00 private-config.text 5 -rwx 14562176 Jan 1 2015 13:28:19 -06:00 c2960s-universalk9-mz.150-2.SE6.bin 8 -rwx 3096 Jan 17 2018 12:06:38 -06:00 multiple-fs 6 -rwx 64869 Jan 17 2018 12:06:37 -06:00 config.text 57931776 bytes total (43171840 bytes free) 

If I run 'sh startup-config' it just comes up blank.

How do I tell if nvram is corrupt? Would this indicate nvram on the stack master is corrupt, on a single other switch, or on all switches?

I can't just reboot the stack and have it come up corrupt and unable to boot, as this is a 24/7 medical facility.